1. Field of the Invention
The present invention relates to a surface-treating composition and a surface treatment method for metallic material, particularly galvanized sheet metal, and provides an anticorrosive composition for conferring adequate anticorrosion on metallic material.
2. Description of the Related Art
In an atmosphere containing salts such as seawater or in an atmosphere of high-humidity and high-moisture, galvanized sheet metal and alloyed galvanized sheet metal generate white rust on the surface to be deteriorated in appearance, thus reducing e.g. their ability to prevent rust from occurring on iron surfaces as substrates.
Conventionally, chromate-type anticorrosion treatment compositions have been often used to prevent white rust, for example, Japanese Patent Application KOKAI No. 131370/1991 discloses a resin-type treatment composition having a water-dispersible chromium compound and a water-dispersible silica contained in a dispersion of an olefin-.alpha., .beta.-ethylenically unsaturated carboxylic acid copolymer.
However, even the above chromium-containing, resin-type treatment composition is not necessarily adequate in corrosion-resistance and white rust which occurs upon long exposure to salt solution or to atmosphere of high-temperature and high-humidity. Demand for non-chromium anticorrosive treatment composition is increasing in recent years.
It has been found that sulfide ions reacting with zinc to form a stable film of ZnS and non-chromium anticorrosive treatment compositions containing sulfides and sulfur was disclosed in Japanese Patent Application KOKAI Nos. 239776/1996 and 678341/1996.
However, some sulfides have peculiar odors and their handling is not necessarily easy.
Further, anticorrosive treatment compositions containing sulfur-containing, odorless and nontoxic triazine thiol compounds are also proposed. For example, Japanese Patent Application KOKAI No. 31737/1978 ("Water-Soluble Anticorrosive Paint") discloses a water-soluble anticorrosive paint to which dithiol-S-triazine derivatives are added.
Further, Japanese Patent Application KOKAI No. 223062/1986 ("Reactive Emulsion with Metal") discloses an emulsion reactive with metal obtained by mixing a thiocarbonyl group-containing compound with a water-sparingly-soluble or water-insoluble organic compound.
However, the object of the above water-soluble anticorrosive paint disclosed in Japanese Patent Application KOKAI No. 31737/1978 lies in anticorrosion of soft steel, Copper, brass, copper wire etc., and particularly the paint is prepared such that it can easily adhere to a material whose substrate is copper or brass. Accordingly, it was insufficient as the anticorrosive composition for metallic surfaces such as zinc etc.
Further, the above reactive emulsion disclosed in Japanese Patent Application KOKAI No. 223062/1986 is an emulsion reacting with copper, nickel, tin, cobalt, aluminum etc. and alloys thereof, so it is also inadequate as an anticorrosive composition for metallic surfaces such as zinc etc.
It has been studied that a triazine thiol-containing anticorrosive coating composition is also effective for anticorrosion of galvanized sheet metal, and as described in Japanese Patent Application No. 2557/1997. However, triazine thiol is an expensive compound, so a cheaper anticorrosive treatment composition was desired.
Japanese Patent Application KOKAI Nos. 71734/1979 and 326584/1991 disclose methods for surface-treatment of zinc or zinc alloys with a composition containing neither chromium nor triazine thiol. Japanese Patent Application KOKAI No. 71734/1979 discloses a method of surface-treatment of zinc or zinc alloys, which comprises treating the surface of zinc or zinc alloys with an aqueous solution containing 0.5 to 100 g/l of an ester of two to six phosphoric acids or salts thereof with myo-inositol, 0.5 to 30 g/l (in terms of metal content) of one or more members selected from the group consisting of titanium fluorides and zirconium fluorides, and 1 to 50 g/l of thiourea and/or derivatives thereof. This prior art requires titanium fluorides or zirconium fluorides to form a passive film as a protective layer on a zinc surface. Japanese Patent Application KOKAI No. 226584/1991 discloses a surface-treatment agent which is an aqueous solution of pH value of 5 to 10 containing at least 0.02 g/l of Ni.sup.2+ and/or Co.sup.2+, ammonia and one or more compounds having primary amine groups. This prior art requires Ni.sup.2+ and/or Co.sup.2+, because the adhesion of the coat and anticorrosion after the coat are achieved by the deposition of the cobalt or nickel. The treatment agent containing metallic ions as described above is inconvenient for waste-water treatment etc. because of environmental pollution.